Especially at the fastest settings, intra analysis was taking up the majority of MB analysis time.
This patch takes a ton more shortcuts at the fastest encoding settings, decreasing compression 0.5-5% but improving speed greatly.
Also rearrange the fastest presets a bit: now we have ultrafast, superfast, veryfast, faster.
superfast is the old veryfast (but much faster due to this patch).
veryfast is between the old veryfast and faster.
faster is the same as before except with MB-tree on.

Encoding with subme >= 5 should be unaffected by this patch.